Process for obtaining copper alloys

ABSTRACT

THE DISCLOSURE TEACHES A METHOD OF PREPARING COPPER ALLOY HAVING IMPROVED TOUGHNESS AND STRESS CORROSION RESISTANCE. THE PROCESS COMPRISES: PROVIDING A COPPER ALLOY CONTAINING FROM 12.5 TO 30% NICKEL, 12.5 TO 30% MANGANESE, BALANCE COPPER; HOT ROLLING SAID ALLOY WITH A STARTING TEMPERATURE IN THE RANGE OF 780 TO 900*C.; COLD ROLLING SAID ALLOY; AND ANNEALING SAID ALLOY AT A TEMPERATURE OF FROM 550 TO 900*C. FOR AT LEAST ONE MINUTE WHILE MAINTAINING AN AVERAGE GRAIN SIZE OF LESS THAN 0.015 MM.

1973 s. SHAPIRO ETAL 3,712,337

PROCESS FOR OBTAINING COPPER ALLOYS Filed Nov. 5, 1971 400 I I I I I ALLOY A fi Q S- ALLOY c Q; 100- a L ALLOYD s a e e- I40 I I I80 200 2/0 0.2 "A 0rFsr YIELD Smmcm (KSO 'mvsmons srA/vLer .SHAP/RO ALAN J. GOLDMAN' DERK E. TYLER RICHARD 0 A/vAM BY W ATTORNEY United States Patent PROCESS FOR OBTAINING COPPER ALLOYS Stanley Shapiro, New Haven, Conn., Alan J. Goldman,

Silver Spring, Md, and Derek E. Tyler, Cheshire, and

Richard D. Lanaln, Harnden, (101111., assignors to Olin Corporation Filed Nov. 5, 1971, Ser. No. 196,006 Int. Cl. C22f 1/08 US. Cl. 148--11.5 R Claims ABSTRACT OF THE DISCLOSURE The disclosure teaches a method of preparing copper alloy having improved toughness and stress corrosion resistance. The process comprises: providing a copper alloy containing from 12.5 to 30% nickel, 12:5 to 30% manganese, balance copper; hot rolling said alloy with a starting temperature in the range of 780 to 900 0.; cold rolling said alloy; and annealing said alloy at a temperature of from 550 to 900 C. for at least one minute while maintaining an average grain size of less than 0.015 mm.

BACKGROUND OF THE INVENTION Copper base alloys are known which contain relatively large amounts of nickel and manganese. Alloys of this type are highly desirable since they are capable of obtaining yield strengths in excess of 200K s.i. upon aging. In addition, these alloys appear to have reasonable processing and in particular are not quench sensitive.

The presence of a marked aging response to obtain high strengths in copper-nicked manganese alloys is known. It has been found that different types of precipitation reactions may occur in this alloy system, depending on the aging temperature. For example, aging at a low temperature, such as 350 C., yield a cellular precipitate which nucleates at the grain boundaries and with time grows throughout the entire grain. The cellular precipitate consists of adjacent lamellae of a manganese-nickel rich phase and the copper-rich solid solution. Aging at higher temperatures, such as 450 C., yields mainly finely dispersed, spherical precipitates of the manganese-nickel rich phase within the grains and only a small amount of the cellular precipitate at the grain boundaries.

However, in any event, the presence of a cellular precipitate at grain boundaries is generally found to. have deleterious effects on alloy properties, such as fracture toughness and stress corrosion resistance. This is indeed found to be the case in these alloys and is a significant factor in the limited commercial success which these alloys have enjoyed.

It would be highly desirable to develop a method for processing the copper-manganese-nickel alloys which provides increased fracture toughness. It would also be highly desirable to improve the stress corrosion resistance of such alloys.

Accordingly, it is a principal object of the present invention to develop a method for processing copper base alloys containing relatively large amounts of nickel and manganese, which method provides improved properties.

It is an additional object of the present invention to develop a process as aforesaid which is capable of obtaining excellent yield strengths upon aging, for example, yield strengths in excess of 200K s.i.

It is a still further object of the present invention to develop a process as aforesaid which is readily practiced commercially and which is characterized by providing improved fracture toughness.

It is a still further object of the present invention to provide a process which provides copper base alloys with 3,712,837. Patented Jan. 23, 1973 good stress corrosion resistance, good ductility, toughness and excellent yield strength characteristics.

Further objects and advantages of the present invention will appear from the ensuing discussion.

SUMMARY OF THE INVENTION In accordance with the present invention, it has now been found that the foregoing objects and advantages may be readily obtained.

The process of the present invention comprises: providing a copper base alloy containing from 12.5 to 30% nickel, from 12.5 to 30% manganese, balance copper, wherein the nickel to manganese ratio is at least 0.75 and preferably 1.0 or higher; hot rolling said alloy with a starting hot rolling temperature in the range of 780 to 900 C., cold rolling said alloy, and annealing said alloy at a temperature of from 550 to 900 C. for at least one minute while maintaining an average grain size of less than 0.015 mm.

BRIEF DESCRIPTION OF DRAWINGS The drawing which forms a part of the present specification is a graph plotting the fracture toughness as a function of yield strength for various alloys, representing the properties longitudinal to the rolling direction.

DETAILED DESCRIPTION In accordance with the present invention, the foregoing process has been found to obtain surprisingly improved fracture toughness while retaining the excellent strength characteristics of this alloy system.

This enables the attainment of several significant advantages. The alloys which are obtained in accordance with the present invention are excellent lower priced replacements for beryllium-copper, with increased fracture toughness. The alloys achieve levels of fracture toughness approaching high alloy steels which are limited in applicability by poor corrosion resistance. The alloys are superior to maraging steels in marine environments since the alloys obtained in accordance with the present invention are not susceptible to hydrogen embrittlement. In addition, the alloys provided pursuant to the instant process are characterized by excellent stress corrosion resistance.

In accordance with the present invention, the starting alloys contain from 12.5 to 30% nickel, and from 12.5

'to 30% manganese. Preferably, both the nickel and manganese contents should range from 15 to 25%. The nickel to manganese ratio must be at least 0.75 and preferably 1.0 or higher.

The nickel and manganese contents have an affect on aging response, yield strength and workability of the alloys. The lower the manganese and nickel content, the slower the aging response and lower the maximum yield strength obtainable upon aging, especially below 12.5% nickel and manganese. On the other hand, increasing the amount Olf nickel and manganese has deleterious effects on the workability of the alloys during processing, especially over 30% each of nickel and manganese.

As indicated hereinabove, the preferred nickel to manganese ratio is 1.0 or higher. The maximum aging response is obtained for a given amount of nickel and manganese when the nickel to manganese ratio is about 1.0. If the ratio is less than 1.0, an excess of manganese exists which can have adverse effects on the stress corrosion resistance of the alloy. A ratio greater than about 1.5 does not give improved results over a ratio of about 1.0 and is more expensive due to the high cost of the nickel.

In addition to the foregoing, it is preferred that the starting alloys contain certain alloying additions. These alloying additions will be described hereinbelow and they may be present either separately or in combination.

It is preferred that the alloy contain a material selected from the group consisting of aluminum in an amount from 0.01 to 5.0%, magnesium from 0.01 to 5.0%, boron from 0.001 to 0.1% and mixtures thereof. Each of these elements act as deoxidizers and assist in the melting of the alloys. Aluminum is the preferred addition since it tends to form a protective oxide coating during melting. When aluminum is used as a deoxidant only, the aluminum should be added in an amount from 0.01 to 0.75%. Similarly, magnesium should be used in an amount from 0.01 to 0.75% as a deoxidant. In addition, the aluminum and magnesium may be used as advantageous alloying additions in amounts greater than 0.6% for increased corrosion resistance and fracture toughness. The aluminum when used at the higher levels, also tends to modify the cellular precipitate at the grain boundaries.

In addition a zinc component may be present in an amount from 0.1 to 3.5% and preferably from 1 to 3%. Increased amounts of zinc give rise to a decrease in the stress corrosion resistance and fracture toughness.

The zinc addition controls the grain size, reduces the cellular precipitate at the grain boundaries, changes the morphology of the inclusions, promotes sound castings and increases the aging response of the alloy.

Tin is also a particularly desirable additive in an amount from 0.01 to 2% and preferably from 0.5 to 1.0%. Tin tends to alter the morphology of the cellular precipitate at the grain boundary.

In addition, zirconium and/or titanium are preferred alloying additions in amounts 0.01 to 2.0% each, and preferably from 0.15 to 0.30% each. These materials tend to desirably change morphology and chemistry of inclusions and desirably change morphology of cellular precipitate at grain boundaries.

In addition, chromium is a desirable addition in an amount from 0.01 to 1.0%, and preferably from 0.15 to 0.30%. Chromium tends to control the grain size and change the morphology and chemistry of inclusion.

Additional desirable alloying additions are cobalt and/ or iron in amounts from 0.05 to 1.0% each, and preferably from 0.2 to 0.5% each. These materials also tend to control the grain size.

Therefore, it can be seen that in addition to the required nickel and manganese components, the alloys desirably utilize a material selected from the group consisting of aluminum, magnesium, boron, zinc, tin, zirconium, titanium, chromium, cobalt, iron and mixtures thereof, all in the amounts listed hereinabove.

Naturally, other additives may be desirable in order to achieve or accentuate a particular property and conventional impurities may be tolerated.

The casting of the alloy of the present invention is not particularly significant. Any convenient method of casting may be employed. Pouring temperatures in the range of about 1000 to 1200 C. are preferably employed, with an optimum pouring temperature in the range of 1050 to 1100 C.

Generally, the alloy of the present invention is processed by breakdown of ingot into strip using a hot rolling operation followed by cold rolling and annealing cycles to reach final gage. Preferred properties are obtained using an aging treatment.

The starting hot rolling temperature should be in the range of 700 to 900 C., and preferably 780 to 900 C. The cooling rate from hot rolling should preferably be in excess of 25 C. per hour down to 300 C. in order to avoid precipitation of manganese-nickel rich phases. The cooling rate after 300 C. is not significant. The alloy is capable of cold rolling reductions in excess of 90%, but the cold rolling reduction should preferably be between 30 and 80% in order to control the grain size.

It has been found that an average grain size less than 0.015 mm. is required to give the optimum fracture toughness. An average grain size of this order can be obtained by control of the cold rolling reduction, annealing times and annealing temperatures. In general, annealtemperatures in the range of 550 to 900 C. for at least one minute can give the required grain size, with 10* hours being the practical upper limit and 2 hours being the preferred upper limit. It is preferred to anneal for from five minutes to 2 hours.

After annealing, the material is cooled in excess of 25 C. per hour down to 300 C., as indicated above, and the cold rolling and annealing cycles repeated as desired depending on gage requirements. Generally, from two to four cycles of cold rolling and annealing are preferred.

In accordance with the present invention, it has been found that certain annealing relationships are significant in order to provide the desired properties. These relationships generally indicate what the maximum annealing time should be in order to maintain the grain size at or below 0.015 mm.

Thus, in accordance with the present invention, where the alloy contains zinc, as indicated hereinabove, the following relationship X exists:

and where the alloy does not contain zinc as indicated hereinabove, the following relationship Y exists:

wherein in both cases ln=the natural logarithm t=the annealing time in minutes to obtain an average grain diameter of 0.015 mm.

T=the temperature in degrees Kelvin C=the percent that the material was cold rolled Hence, for example, calculations performed utilizing relationship X, cold rolled 60% gave the following results:

at 600 C., t=287 minutes at 625 C., t=83 minutes at 650 C., t=35 minutes In accordance with the present invention, it is preferred to perform an aging operation. The alloy of the present invention, as previously stated, may be aged in the range of 250 to 475 C., with temperatures of 380 to 460 C. being preferred. Aging times of 30 minutes to 10 hours, with preferred times of 1 to 6 hours, are used to obtain the desired properties. -In addition, it has been found that controlling the amount of cold work prior to aging has an effect on fracture toughness and aging response. In particular, it has been observed that the cold work gives rise to increased nucleation sites for the intragranular precipitation of the discrete manganese-nickel rich particles. Hence, cold working of the alloys prior to aging at the higher temperatures of the aging range increases the aging response and decreases the amount of cellular precipitate. The amount of cold rolling can vary from 10 to 50% with from 15 to 45% yielding the optimum fracture toughness.

The present invention will be more readily understandable from a consideration of the following illustrative examples.

EXAMPLE I The Durville method was used to cast the various alloys listed in Table I. The copper and nickel were melted under a charcoal cover. Aluminum was added to deoxidize the melt. Following the removal of the charcoal cover, the manganese and zinc additions were made. The slag was removed and the melt was poured from approximately 1080 C.

TABLE L--COMPOSITION, WEIGHT PERCENT The alloys prepared in Example I were processed in the following manner. Alloys A and B were homogenized at 840 C. for about 2 hours, followed by hot rolling from 1.500 inches to 0.418 inch and water quenching. The alloys were cold rolled 60% to 0.167 inch. Alloys A and B were then annealed at 600 C. for about 30 minutes and water quenched. The alloys were cold rolled 60% to 0.067 inch and annealed and quenched again in the same manner. Subsequent to the water quench, the alloys were cold rolled 25% to 0.050 inch and aged at 450 C. for various times.

Alloys C and D were homogenized at 840 C. for about 2 hours, followed by hot rolling from 1.500 inches to 0.320 inch and water quenching. The alloys were cold rolled 62.5% to 0.120 inch. Alloys C and D were then annealed at 650 C. for about 60 minutes. The alloys were cold rolled 44% to 0.067 inch and were again annealed at 650 C. for about 60 minutes. Subsequent to the water quench, the alloys were cold rolled 25% to 0.050 inch and aged at 450 C. for various times.

The resultant properties were determined after various aging times. These are indicated in Table II which represents the properties longitudinal to the rolling direction. The term UPE is a relative value of the fracture toughness determined by the Kahn Tear Test.

The variations in cold reduction, annealing temperatures and annealing times resulted in variations in the grain size of the alloys. Alloys A and B had an average grain diameter of 0.005 to 0.010 mm. Alloy C had an average grain diameter of 0.024 mm, and Alloy D 0.022 mm. The resulting properties longitudinal to the rolling direction upon aging at 450 C. are presented in Table 11.

TABLE IL-LONGITUDINAL PROPERTIES Yield strength, 0.2% ofiset, UPE, in. K s.i. Ill/1D.

The data are presented in graphical form in FIG. 1. The UPE is plotted as a function of yield strength for Alloys A, B, C and D. For a given yield strength, the superiority of the fine grained material processed in accordance with the present invention is quite graphic.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A method of preparing copper base alloys having improved toughness and stress corrosion resistance which comprises:

(A) providing a copper base alloy containing from 12.5 to 30% nickel, from 12.5 to 30% manganese, balance copper, wherein the nickel to manganese ratio is at least 0.75;

(B) hot rolling said alloy with a starting hot rolling temperature in the range of 700 to 900 C.;

(C) cold rolling said alloy; and

(D) annealing said alloy at a temperature of from 550 to 900 C. for at least one minute while maintaining an average grain size of less than 0.015 mm.

2. A method according to claim 1 wherein said copper base alloy contains a material selected from the group consisting of: aluminum from 0.01 to 5%; magnesium from 0.01 to 5 boron from 0.001 to 0.1%; zinc from 0.1 to 3.5%; tin from 0.01 to 2% zirconium from 0.01 to 2%; titanium from 0.01 to 2%; chromium from 0.01 to 1%; iron from 0.05 to 1%; cobalt from 0.05 to 1%; and mixtures thereof.

3. A method according to claim 1 wherein said alloy is cast utilizing a pouring temperature of from 1000 to 1200 C.

4. A method according to claim 1 wherein said material is cooled after hot rolling utilizing a cooling rate in excess of 25 C. per hour down to at least 300 C,

5. A method according to claim 4 wherein said cold reduction is from 30 to 80%.

6. A method according to claim 5 wherein said annealing time is from 5 minutes to 2 hours.

7. A method according to claim 1 wherein from two to four cycles of cold rolling and annealing are employed.

8. A method according to claim 2 wherein the maximum annealing time is in accordance with the following formulae:

when the alloy contains zinc,

and when no zinc is present 1 In =27.150.120C-- T References Cited UNITED STATES PATENTS 824,103 6/ 1906 Driver l59 981,542 l/191l Driver 75l59 3,224,875 '12/1965 Buehler et al. 75l59 FOREIGN PATENTS 577,170 5/194'6 Great Britain 75l59 660,964 ill/1951 Great Britain 75l59 395,720 7/ 1933 Great Britain 75l59 WAYLAND W. STALLARD, Primary Examiner U.S. Cl. X.R. 148-127 

